578 PR A GMENT8 OF SCTENCK. 



as to prompt the conclusion that the apparently pure flame of the 

 alcohol-lamp required but a beam of sufficient intensity to reveal its 

 clouds of liberated carbon. 



But is the blackness smoke? This question presented itself in a 

 moment, and was thus answered: A red-hot poker was placed under- 

 neath the beam; from it the black wreaths also ascended. A large 

 hydrogen flame, which emits no smoke, was next employed, and it 

 also produced with augmented copiousness those whirling masses of 

 darkness. Smoke being out of the question, what is the blackness? 

 It is simply that of stellar space; that is to say, blackness resulting 

 from the absence from the track of the beam of all matter competent 

 to scatter its light. When the flame was placed below the beam, the 

 floating matter was destroyed in situ; and the heated air, freed from 

 this matter, rose into the beam, jostled aside the illuminated particles, 

 and substituted for their light the darkness due to its own perfect 

 transparency. Nothing could more forcibly illustrate the invisibility 

 of the agent which renders all things visible. The beam crossed, un- 

 seen, the black chasm formed by the transparent air, while, at both 

 sides of the gap, the thick-strewn particles shone out like a luminous 

 solid under the powerful illumination. 



Supposing an infusion intrinsically barren, but readily 

 susceptible of putrefaction when exposed to common air, to 

 be brought into contact with this nnilluminable air, what 

 would be the result? It would never putrefy. It might, 

 however, be urged that the air is spoiled by its violent cal- 

 cination. Oxygen passed through a spirit lamp flame is, 

 it may be thought, no longer the oxygen suitable for the 

 development and maintenance of life. We have an easy 

 escape from this difficulty, which is based, however, upon 

 the unproved assumption that the air has been affected by 

 the flame. Let a condensed beam be sent through a large 

 flask or bolthead containing common air. The track of the 

 beam is seen within the flask the dust revealing the light, 

 and the light revealing the dust. Cork the flask, stuff its 

 neck with cotton-wool, or simply turn it mouth downward 

 and leave it undisturbed for a day or two. Examined 

 afterward with the luminous beam, no track is visible; the 

 light passes through the flask as though a vacuum. The 

 floating matter has abolished itself, being now attached to 

 the interior surface of the flask. Were it our object, as it 

 will be subsequently, to effectually detain the dirt, we might 

 coat that surface with some sticky substance. Here, then, 

 without " torturing " the air in any way, we have found 

 a means of ridding it, or rather of enabling it to rid itself, 

 of floating matter. 



